An aluminum electrolytic capacitor including an electrolyte solution consists of an anode made of aluminum having aluminum oxide as a dielectric on the surface, a cathode as a current collector, and a separator holding the electrolyte solution between the anode and the cathode, all enclosed in a sealed casing. Wound or laminated aluminum electrolytic capacitors are widely known. In these capacitors, the electrolyte solution directly contacts the dielectric and acts as the true cathode. The type of the electrolyte solution thus greatly affects the characteristics of the aluminum electrolytic capacitor.
In electrolytic capacitors, polar solvents (e.g., ethylene glycol) and ammonia salts of azelaic acid or 1,6-decanedicarboxylic acid are widely used (for example, see Patent Literature 1). It is known to further add polyvinyl alcohol or polyoxyethylene glycol to such electrolyte solutions in order to increase spark voltage (for example, see Patent Literature 2).
Unfortunately, polyvinyl alcohol is insoluble in polar solvents (e.g., ethylene glycol), thus making the resulting electrolyte solutions non-uniform. Such electrolyte solutions become more viscous when heated, and thus will be problematic for applications at high temperatures. In addition, polyoxyethylene glycol having a low molecular weight exhibits less improving effect on spark voltage, and polyoxyethylene glycol having a high molecular weight disadvantageously decreases conductivity.